Application of ensemble method to predict radiation doses from a radioactive release during hypothetical severe accidents at Russian NPP

We report an ensemble approach applied to the radiation dose modeling for a hypothetical radiation emergency with a long-term release of radioactive materials into the atmosphere. The study is aimed at improving the emergency response system in Russia and focuses on quantifying the impact of meteorological uncertainties on modeling the atmospheric dispersion and transport. Four sets of options of meteorological conditions are used: (1) classic global weather forecast (zero member), (2) ensemble global weather forecast with 21 members, (3) global weather analysis, and (4) real local weather measurements. The numerical experiments have been conducted for four dates during September-October 2019 using the SOCRAT code for source term evaluation, WRF-ARW model - for weather prediction, and NOSTRADAMUS code - for atmospheric dispersion modeling and dose calculations. The comparable results have been obtained for all performed numerical experiments. The paper presents the results for a hypothetical release on 17 October 2019, but all conclusions are valid for all investigated dates. The ensemble approach has demonstrated to increase significantly the reliability of radionuclide dispersion predictions for severe accident conditions. (author)